Solvent extraction of mineral oils



Nov. 30, 1954 l. w. MILLS 2,695,863

SOLVENT EXTRACTION OF MINERAL OILS Filed April 18, 1950 Oil A (Relatively High V.l.)

Solvent Extraction Raffinate A Extract A Oil B (Relatively Low V.l)

Solvent Extraction Ralfiate B Extract B INVENTOR.

IVOR W. MILLS ATTORNEYS United States Patent SOLVENT EXTRACTION 0F MINERAL OILS Ivor W. Miils, Glenolden, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Appiication April 18, 1950, Serial No. 156,678

4 Claims. c1. 196-1448) This invention relates to solvent extraction of mineral oils, such as petroleum distillate and residual oils, and more particularly concerns a procedure for extracting two independent charge oils which have, respectively, relatively high and relatively low viscosity indexes.

In the petroleum refining art solvent extraction has been widely used for the purpose of treating oils to obtain products of higher viscosity index. Numerous solvents are known for this purpose. Such solvents are capable of preferentially dissolving aromatic constituents from the charge, so that the treatment results in an aromatic-rich extract of low viscosity index and an aromatic-lean raflinate which. has a viscosity index higher than the charge. Examples of known solvents are furfural, sulfur dioxide, nitrobenzene, phenol, B-B dichlorethyl ether, and cresylic acid-propane.

In commercial refinery practice, it frequently happens that several different charge oils derived from crudes of varying types are subjected to such solvent refining. Some stocks to be treated, for instance, may have been obtained from so-called naphthenic base crudes and therefore have relatively low viscosity indexes, while others may have been derived from mixed base or paraffinic base crudes and thus initially have relatively high viscosity indexes as compared to the naphthenic base stocks. In the usual practice these charge oils are extracted in operations which are entirely independent of each other to yield raliinate and extract products. The extract products usually contain aromatics to the extent of say 60-85%, inasmuch as the extraction conditions which are necessary for producing extract material of still higher aromatic content generally would constitute uneconomic practice for commercial refining.

I have now found that in the extraction of two independent charge oils having relatively low and relatively high viscosity indexes, respectively, an improved rafiinate product can be produced in treatment of the low viscosity index stock by utilizing an integrated extraction procedure as hereinafter fully described. The improvement provided by employing such procedure can be reflected with respect either to higher viscosity index for a given yield of the ratiinate product or to higher yield of the ratfinate product for a given viscosity index, as compared to the results obtained in the usual practice of conducting the extractions as wholly independent operations.

According to the invention the charge stock of relatively high viscosity index is first extracted in the usual manner to yield a rafiinate product and an aromatic-rich extract product. The latter is then blended with the charge stock of relatively low viscosity index and the blend is extracted to separate an aromatic-rich extract and thereby obtain the improved rafiinate product.

The procedure according to the invention is illustrated schematically in the accompanying drawing in which the two charge oils are designated as oil A and oil B. Oil A is one which initially has a relatively high viscosity index and may, for example, be a distillate or residuum stock obtained from a crude oil of the paraffin base type or mixed base type, such crudes being characterized by viscosity-gravity constants below about 0.86. Oil B is one of relatively low viscosity index, for example, a distillate or residuum derived from a naphthenic base type crude, which type characteristically possesses a viscosity-gravity constant above about 0.86.

The first step in the procedure comprises subjecting oil A to solvent extraction, as indicated schematically at It) in the accompanying drawing, to obtain rafiinate A and aromatic-rich extract A. Using commercially feasible extraction conditions, the latter generally will. have an aromatic content of the order of 6085%. Extract A is then blended with oil B and the mixture is solvent extracted, as indicated at 11, to yield rafiinate B and aromatic-rich extract B. The aromatic content of extract B again will be of the order of 6085%. On the other hand, rafiinate B will have a higher viscosity index than would a raffinate produced in the same amount by extraction of oil B alone; or alternatively a larger amount of rafiinate will be obtained if the second extraction step is conducted so as to obtain the same viscosity index as would be obtained by extraction of oil B alone.

In each of the extraction steps of the foregoing process, any known or suitable solvent capable of preferentially dissolving aromatic hydrocarbons from the charge material can be employed, and it is to be understood that the invention does not necessarily reside in the use of any particular extraction solvent. In fact, the process may also be practiced utilizing selective adsorption in place of the solvent extraction steps, for example, by treating the charge materials with an adsorbent such as silica gel or activated carbon to obtain aromatic-rich and aromatic-lean products which are equivalent to the extract and rafiinate products from solvent extraction.

The following example is illustrative:

A distillate oil derived from mixed base crude oil was extracted with furfural, thereby yielding rafiinate and extract products. Properties of the charge oil and of the products, and yields of the products, are shown in the following table:

Charge Rafiinate Extract Yield, percent of charge oil 76 24 A. P. I. it 27.0 31.9 13.4 S U Vise. at 100 F 234 163 1834 S. U. vise. at 210 F 47. 6 44. 6 71.9 Viscosity index +108 -91 Aromatic content, percent by vol 75 g Raifinate Yield, percent (based on distillate oil) (approx) 931.

S. U. vise. at 100 F 1, 569

S. U. vise. at 210 F. 73. 3 64. 7. Viscosity index -37 +7. Aromatic content, percent 47 46 These results show that the treatment resulted in an upgrading of the naphthenic distillate oil from a material having a viscosity index or" minus 37 to one having a viscosity index of plus 7, without any substantial loss in volume. This was so even though the aromatic contents of the distillate oil and rafiinate were about the same. It is apparent that if the second extraction step were conducted so as to obtain a lower yield of rafiinate, a still higher viscosity index of the raitinate product would be obtained.

While the two charge oils used in the foregoing specific example were distillate fractions, it is to be understood that the invention can be practiced with charge oils either or both of which are residuum stocks or mixtures of distillate and residuum stocks.

I claim:

1. Method which comprises solvent extracting a lubricating oil stock derived from mixed base crude oil to separate an aromatic-rich extract, blending said aromaticrich extract, essentially free of solvent, with a lubricating oil stock as obtained by distillation from naphthenic base crude oil and having a viscosity index which is relatively low compared to that of the first-mentioned stock but higher than that of said aromatic-rich extract and then solvent extracting the blend to obtain an aromatic-rich extract and a rafiinate product, whereby said rafiinate product has a higher viscosity index than is obtainable, for the same amount of raffinate product, from the lastnamed lubricating oil stock alone.

2. In a method for solvent extracting a relatively low viscosity index lubricating oil stock derived from crude oil of relatively high viscosity-gravity constant to separate an aromatic-rich extract from a rafiinate product, the improvement which comprises mixing said lubricating oil stock, as obtained by distillation from crude oil of relatively high viscosity-gravity constant, with a substantially solvent-free aromatic-rich extract obtained from a relatively high viscosity index lubricating oil stock derived from crude oil of relatively low viscosity-gravity constant, said aromatic-rich extract having a lower viscosity index than the said lubricating oil stock with which it is mixed and then extracting the mixture, whereby the resulting ratfinate product has a higher viscosity index than is obtainable, for the same amount of raffinate product, from said low viscosity index stock alone.

3. Method which comprises solvent extracting a relatively high viscosity index lubricating oil stock derived from crude oil of relatively low viscosity-gravity constant to separate an aromatic-rich extract, blending said aromatic-rich extract, substantially free of solvent, with a relatively low viscosity index lubricating oil stock as obtained by distillation from crude oil of relatively high viscosity-gravity constant and having a viscosity index which is relatively low compared to that of the firstmentioned stock but higher than that of said aromaticrich extract, and then solvent extracting the blend to obtain an aromatic-rich extract and a rafiinate product, whereby said rafiinate product has a higher viscosity index than is obtainable, for the same amount of raflinate product, from the last-named lubricating oil stock alone.

4. Method according to claim 3 wherein the firstnamed lubricating oil stock is derived from crude oil having a viscosity-gravity constant below 0.86 and the last-named lubricating oil stock is derived from crude oil having a viscosity-gravity constant above 0.86.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,788,569 Ferris Ian. 13, 1931 1,899,969 Kurtz Mar. 7, 1933 2,024,476 Rutherford Dec. 17, 1935 2,070,384 Tuttle Feb. 9, 1937 2,091,078 McKittrick et al. Aug. 24, 1937 2,165,638 Manley July 11, 1939 2,201,549 Van Dijck May 21, 1940 2,201,550 Van Dijck et a1 May 21, 1940 2,220,016 Lyons Oct. 29, 1940 2,270,827 Tijmstra Jan. 20, 1942 2,330,054 Hibshman Sept. 21, 1943 

1. METHOD WHICH COMPRISES SOLVENT EXTRACTING A LUBRICATING OIL STOCK DERIVED FROM MIXED BASE CRUDE OIL TO SEPARATE AN AROMATIC-RICH EXTRACT, BLENDING SAID AROMATICRICH EXTRACT, ESSENTIALLY FREE OF SOLVENT, WITH A LUBRICATING OIL STOCK AS OBTAINED BY DISTILLATION FROM NAPHTHENIC BASE CRUDE OIL AND HAVING A VISCOSITY INDEX WHICH IS RELATIVELY LOW COMPARED TO THAT OF THE FIRST-MENTIONED STOCK BUT HIGHER THAN THAT OF SAID AROMATIC-RICH EXTRACT AND THEN SOLVENT EXTRACTING THE BLEND TO OBTAIN AN AROMATIC-RICH EXTRACT AND RAFFINATE PRODUCT WHEREBY SAID RAFFINATE PRODUCT HAS A HIGHER VISOCITY INDEX THAN IS OBTAINABLE FOR THE SAME AMOUNT OF RAFFINATE PRODUCT, FROM THE LAST, NAMED LUBRICATING OIL STOCK ALONE. 